package com.liu.circle;

import com.liu.AbstractList;

/**
 * @author liucong
 * @date 2021/2/15 - 16:46
 */
public class CircleLinkedList<E> extends AbstractList<E> {
    private Node<E> first;
    private Node<E> last;

    private static class Node<E>{
        E element;
        Node<E> prev;
        Node<E> next;

        public Node(Node<E> prev,E element, Node<E> next) {
            this.prev=prev;
            this.element = element;
            this.next = next;
        }

        @Override
        public String toString() {
            StringBuilder sb=new StringBuilder();

            if(prev!=null){
                sb.append(prev.element);
            }else{
                sb.append("null");
            }

            sb.append("_").append(element).append("_");

            if(next!=null){
                sb.append(next.element);
            }else{
                sb.append("null");
            }

            return sb.toString();
        }
    }

    /*
    gc root对象
    （1）被栈指针（局部变量）指向的对象
     */
    @Override
    public void clear() {
        first=null;
        last=null;
        size=0;
    }

    @Override
    public E get(int index) {
        return node(index).element;
    }

    @Override
    public E set(int index, E element) {
        Node<E> node=node(index);
        E old=node.element;
        node.element=element;
        return old;
    }

    @Override
    public void add(int index, E element) {
        rangeCheckForAdd(index);

        if(index == size){ //往最后面添加元素
            Node<E> oldLast=last;
            last=new Node<>(oldLast,element,first);
            if(oldLast==null){ //链表添加第一个元素
                first=last;
                first.next=first;
                first.prev=first;
            }else{
                oldLast.next=last;
                first.prev=last;
            }
        }else{
            Node<E> next=node(index);
            Node<E> prev = next.prev;
            Node<E> node = new Node<>(prev, element, next);
            prev.next=node;
            if(index == 0){ // index==0
                first=node;
            }
            next.prev=node;
        }

        size++;
    }

    @Override
    public E remove(int index) {
        rangeCheck(index);
        Node<E> node=first;

        if(size == 1){
            first=null;
            last=null;
        }else{
            node = node(index);
            Node<E> prev = node.prev;
            Node<E> next = node.next;

            prev.next=next;
            next.prev=prev;

            if(index==0){ //index==0
                first=next;
            }

            if(index==size-1){ //index==size-1
                last=prev;
            }
        }

        size--;
        return node.element;
    }

    @Override
    public int indexOf(E element) {
        if(element==null){
            Node<E> node=first;
            for (int i = 0; i < size; i++) {
                if(node.element==null)
                    return i;
                node=node.next;
            }
        }else{
            Node<E> node=first;
            for (int i = 0; i < size; i++) {
                if(element.equals(node.element))
                    return i;
                node=node.next;
            }
        }
        return ELEMENT_NOT_FOUND;
    }

    /**
     * 获取index位置对应的节点对象
     * @param index
     * @return
     */
    private Node<E> node(int index){
        rangeCheck(index);

        if(index<(size>>1)){
            Node<E> node=first;
            for(int i=0;i<index;i++){
                node=node.next;
            }
            return node;
        }else{
            Node<E> node=last;
            for(int i=size-1;i>index;i--){
                node=node.prev;
            }
            return node;
        }
    }

    @Override
    public String toString() {
        StringBuilder string = new StringBuilder();
        string.append("size=").append(size).append(", ").append("[");
        Node<E> node = first;
        for (int i = 0; i < size; i++) {
            if(i!=0)
                string.append(", ");
            string.append(node);
            node=node.next;
        }
        string.append("]");
        return string.toString();
    }
}
